The present embodiments relate to a shim coil arrangement with spacers.
Magnetic resonance devices (e.g., MRTs or MRI scanners) for examining objects or patients through magnetic resonance tomography are known, for example, from DE10314215B4.
A known gradient coil system for a magnetic resonance imaging (MRI) scanner includes, for example, three primary coil layers that are capable of generating electromagnetic fields in the three spatial directions x, y, z. The coil layers are, for example, arranged concentrically on a cylinder surface. Three further secondary coil layers are located, for example, at a radial distance. The three further secondary coil layers have the task of generating an opposing field, and thus screening the field components directed outwards as far as possible. Cooling levels through which water flows are located between these coil layers in order to take away the dissipated power deposited in the system. An active shim system between primary and secondary coils may optionally be provided. The active shim system serves to improve the homogeneity of the basic magnetic field of the MRT. This active shim system includes a number of layers of copper coils to which direct current is applied. The complete prefabricated gradient coil structure is impregnated in a vacuum, for example, with a molding resin, and this is hardened. A number of layers of shim coils may be accommodated electrically insulated radially from one another in the space between primary and secondary gradient coils and may be impregnated as completely and error-free as possible with molding resin.
Previously, in accordance with a known method, a single shim layer may be fabricated from a basic material for printed circuit boards. This may include an epoxy-glass laminate, for example, that is glued in a single layer to a copper film of the appropriate thickness. The pre-calculated conductor track structure is manufactured by process acts like those used for circuit board fabrication in an etching process.
Another known method includes winding the desired conductor structure from a round or flat wire into a winding plate and gluing the winding plate to an insulation carrier layer. The carrier layer of the conductor structure possesses a smooth, flat surface in relation to the conductor structure. When a shim board or another smooth surface comes into contact with the carrier layer as a next layer, a defined distance between these concentric surfaces is provided, so that the molding/impregnating resin may completely fill the space between the concentric surfaces.
The distance between the individual shim coil layers and an error-free impregnation is defined, for example, by individual or interconnected rods made from an electrically-insulating material, holes/cutouts in the GFK carrier plate between the conductor tracks (cf., DE102005025340), and circumferential windings with plastic sleeves spaced close to one another.